Project Summary: Rising atmospheric CO2 and global warming could
alter the functioning of terrestrial ecosystems, and a number
of experiments have already been established to document these
potential changes. These experiments have demonstrated some broad
similarities among different ecosystems in their above-ground
responses to these global changes, but whether biogeochemical
responses below-ground exhibit predictable patterns is largely
unknown. For example, elevated CO2 and warming can alter nitrogen
availability to plants and nitrogen inputs to and losses from
ecosystems, but results to date are equivocal, with empirical
support for both increases and decreases in nitrogen availability.
However, because of the short time scale of empirical studies
to date and the different methods used, contrasting results can
not be compared with confidence.

The proposed work will examine how elevated CO2 and warming
alter nitrogen cycling in a broad array of terrestrial ecosystems,
and how these changes will feed back to affect plant and ecosystem
productivity. The research component of this CAREER proposal
comprises: 1) N cycling measurements in CO2 and climate change
experiments, 2) controlled greenhouse experiments, and 3) integration
through modeling. The field experiments will document changes
in N cycling in response to increased temperature and elevated
CO2 using a long-term 15N tracer technique that will reveal time-integrated
effects of these global changes on N cycling. The greenhouse
study will explicitly determine the relative importance CO2-
and warming-induced changes in soil water content for specific
processes in the N cycle, providing a mechanistic underpinning
to the field studies. The modeling integration will explore the
consequences for longer-term ecosystem responses.

This research complements the proposed CAREER teaching and outreach
activities. Observations and experiments (including those proposed
here) along a 3000-m elevational gradient near Northern Arizona
University will serve as the foundation for inquiry-based laboratories
for courses in Ecosystem Ecology and Microbial Ecology. By drawing
on publicity surrounding global change and by providing a scientific
foundation for understanding these topics, these activities are
designed to better engage undergraduate students in the process
of science. This career plan brings together the PI’s interests
in global change research and science education. The research
extends past work on elevated CO2 and carbon and nitrogen cycling
and helps outline a broader long-term objective: to understand
how interactions among element cycles (here, C, N, and H2O) influence
ecosystem processes, including responses to global change. The
proposed teaching activities are designed to place results from
this research – and the research process itself – in
a broader context accessible to the public.

Project Summary: Plant and ecosystem productivity are strongly
influenced by nutrient availability, largely determined by rates
of decomposition of plant litter. Decomposition rates of above-ground
plant tissues (leaves and stems) and associated rates of nutrient
mineralization are well characterized by indices of 'litter quality',
such as nutrient content, carbon:nutrient ratios, or lignin:nutrient
ratios. However, for roots, for reasons that we do not yet understand,
relationships between decomposition rate and such indices of
litter quality are less consistent. Mycorrhizae are ubiquitous
and strongly influence root chemistry, in ways that traditional
indices of litter quality are likely to miss. For these reasons,
including the mycorrhizal status of decomposing roots could substantially
increase our ability to predict root decomposition rates in terrestrial
ecosystems.

Most plant species are associated with soil fungi, forming
root-fungus associations called mycorrhizae. This association
facilitates nutrient and water uptake by plants and provides
carbon through photosynthesis to fungi. Much is known about how
this association affects living roots and whole plants, but the
consequences of mycorrhizal infection for root litter decomposition
have never been investigated. Differences in the degree of mycorrhizal
infection are likely to strongly influence root decomposition
rates, by altering both the carbon and nutrient quality of the
roots for decomposer microorganisms. While mycorrhizae usually
increase nutrient concentrations in all plant tissues by enhancing
nutrient uptake, they also affect root nutrient concentrations
because of the high-nutrient content fungal structures that are
built inside the root as the mycorrhizal association develops.
While high in nutrient content, these structures often contain
a recalcitrant carbon skeleton (e.g., chitin), so that rates
of decomposition are likely to deviate from predictions based
on indices of litter quality.

This project would use greenhouse experiments and natural gradients
in the mycorrhizal status of plants to generate root litter material
from a broad range of species in which the nutrient content and
mycorrhizal status of the root litter vary independently. Following
the characterization of litter for nutrient and carbon 'quality'
(including fractions not typically examined, such as chitin),
mycorrhizal status would be assessed, and decomposition experiments
would be conducted under laboratory and field conditions. Comparing
decomposition rates of litter material from different treatments
would allow a quantitative assessment of the influence of mycorrhizae
and associated changes in root chemistry on root decomposition
rates, and thus has the potential to substantially advance understanding
of the controls over litter decomposition and nutrient availability
in terrestrial ecosystems.

Project Summary: Assessing the effects of restoration on water
and carbon budgets of ponderosa pine forests is critical to predicting
the long-term impacts of restoration on forest productivity and
water use, ecosystem level processes with clear implications
for wildlife, diversity, and links to critical aquatic habitats
in the arid Southwest. If forest productivity increases with
forest restoration, one might expect water use to increase in
concert, as the two are often tightly correlated. Alternatively,
because C4 grasses inhabit the understory in restored stands,
we might expect that the greater water-use efficiency conferred
by this photosynthetic pathway could allow greater forest productivity
with less total stand water use. However, understanding the mechanisms
altering water-use in restored and control stands requires sophisticated
techniques that enable one to partition water use accurately
between trees and understory vegetation, and between plants capable
of more water-use-efficient C4 photosynthesis versus plants that
utilize C3 photosynthesis. In a companion proposal, Kolb, Koch,
and Montes-Helú propose to use sap-flow techniques to
measure tree water use, and understory removal treatments to
assess water use by the understory vegetation. Here, we propose
to complement these efforts by: 1) measuring the source of water
taken up by trees and understory vegetation; 2) determining the
relative contributions of trees and understory vegetation to
total stand water flux, and 3) determine the relative contributions
of trees and understory vegetation to total forest productivity
and respiration. Novel, stable isotope techniques offer a powerful
tool for addressing these questions non-intrusively in restored
and control forest stands. This research will help managers assess
the mechanisms through which forest restoration alters productivity
and water use, and will demonstrate a tool for assessing these
impacts that could be applied in other restoration efforts.

Project Summary. This research integrates field experiments
and models focusing on the responses of a Florida scrub-oak ecosystem
to elevated atmospheric carbon dioxide (CO2). This research adds
to an ongoing study invetigating the effects of elevated CO2
on a naturally-occuring stand of scrub-oak vegetation. The main
goal of the ongoing project is to determine the effects of elevated
CO2 on ecosystem carbon balance. This proposal expands this research
by adding an additional goal: to determine the effects of elevated
CO2 on the water cycle, including plant transpiration, evapotranspiration,
soil moisture, and water table dynamics, as well as how differential
responses of the co-dominant oaks to elevated CO2 mediate these
changes.
In particular, this research will show how the responses of the two co-dominant
oak species in scrub oak mediate reductions in ecosystem water loss through
evapotranspiration, and how these water savings are partitioned between
surface soil water stores and the water table. Transpiration in oak individuals
in elevated and ambient CO2 treatments will be measured in the field,
along with the stable isotope composition of stem water in these species,
which indicates the depth in the soil from which the water is obtained.
Together, these measurements will determine by how much elevated CO2
reduces transpiration, and how that water savings is partitioned in the
soil. This information will be combined with measurements of soil moisture,
water table depth, and evapotranspiration, and synthesized through modeling.
This research is important because it focuses on ecosystem responses
to elevated CO2 that have not been previously addressed, but that will
likely represent critical changes in a future, high-CO2 world. This will
be one of the first studies in any ecosystem to develop a detailed hydrologic
budget and hydrologic model that partitions water savings in elevated
CO2 between surficial and deep water stores in the soil, where savings
will have very different biogeochemical consequences. Additionally, this
research will determine how individualistic species responses to elevated
CO2 mediate changes in system hydrology, and thus will be relevant in
predicting changes in hydrology in other systems where species show differential
responses. By exploring the interactive effects of elevated CO2 through
altered hydrology, this research will substantially advance our knowledge
of the responses of terrestrial ecosystems to rising CO2.

Project Summary. Rising atmospheric CO2 could alter soil nitrogen
(N) cycling, shaping the responses of terrestrial ecosystems
to elevated CO2. Increased carbon input to soil through increased
root growth and increased soil water content due to decreased
plant water use in elevated CO2 can all affect soil N transformations
and thus N availability to plants. This research will determine
the effects of elevated CO2 on nitrogen N cycling in a scrub-oak
ecosystem by using a long-term 15N tracer, and will relate observed
changes in N cycling to changes in carbon input to soil and in
soil hydrology.

Project Summary. This proposal requests funds to purchase an
isotope-ratio mass spectrometer for research in the fields of
Ecology and Environmental Biology at Northern Arizona University
(NAU). This instrument will be used by 15 faculty members in
5 different departments at NAU to address questions such as tracing
energy flow through food webs, determining the fate of environmental
contaminants (e.g., runoff of fertilizaer from agriculture into
aquatic ecosystems), measuring the efficiency with which plants
use water, identifying the sources of water to riparian vegetation,
and measuring turnover of nitrogen and carbon in terrestrial
ecosystems, particularly changes in these processes in response
to environmental perturbation. Use would also include applications
in Archaeology, determining, for example, when human societies
have relied on certain plant species such as corn, which has
a distinctive carbon isotope "signature" that is reflected in
the bones of consumers. Stable isotope techniques allow the investigation
of these questions quantitatively and non-intrusively (without
the environmental hazards of radioisotopes), and thus offer considerable
advantages over other techniques. Indeed, many of these ecological
and environmental questions can only be addressed by using stable
isotopes. Use of these techniques at NAU is severely hampered
by not having ready access to a mass spectrometer facility. The
funds requested in this proposal would relieve this constraint,
and thus greatly enhance research in Ecology and Environmental
Biology at NAU.

Project Summary: We propose an integrated, multidisciplinary
assessment of the impacts of fuel management and restoration
activities on the soil ecosystem in ponderosa pine forests of
the Flagstaff Wildland-Urban Interface. The primary goal of the
research is to determine the consequences of different field
management and restoration activities on key aspects of forest
floor and mineral soil structure and function.

Project Summary: This project will develop an integrated, field-based
ecology curriculum at Northern Arizona University that will involve
undergraduate students (freshmen to seniors) in state-of-the
art research in population, community, and ecosystem ecology.
The core of this project is a new field-based quantitative laboratory
for General Ecology, BIO 326, a course now required by all majors
in Biology, in which students will conduct research along a 3000m
elevational gradient spanning desert to tundra ecosystems as
a natural experiment. Additionally, this project will enhance
introductory biology courses (Introductory Biology and Unity
of Life) by adding field exercises along the gradient, which
will introduce students to the experimental system they will
revisit more comprehensively in General Ecology. The project
will also add advanced exercises involving the gradient to existing
laboratories of a number of upper division courses in ecology
(Entomology, Plant Physiology, Mammalogy, Microbial Ecology,
Ecosystem Ecology, Stable Isotope Techniques, Field Ecology).
Thus, this project will substantially revise and will provide
a unifying theme to the ecology curriculum at Northern Arizona
University: Students will visit the same sites in different courses
and in different years. They will learn how the same systems
and gradients can be approached from different perspectives and
used to address some of the major ecological, environmental and
conservation challenges of our time. This proposal requests funds
to purchase the equipment required to carry out these integrated
laboratories in ecology.